6533b852fe1ef96bd12aad9a

RESEARCH PRODUCT

Optical investigation of spin-crossover in cobalt(II) bis-terpy complexes

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Abstract The spin transition of the [Co(terpy) 2 ] 2+ complex (terpy = 2,2′:6′,2″-terpyridine) is analysed based on experimental data from optical spectroscopy and magnetic susceptibility measurements. The single crystal absorption spectrum of [Co(terpy) 2 ](ClO 4 ) 2 shows an asymmetric absorption band at 14 400 cm −1 with an intensity typical for a spin-allowed d–d transition and a temperature behaviour typical for a thermal spin transition. The single crystal absorption spectra of suggest that in this compound, the complex is essentially in the high-spin state at all temperatures. However, the increase in intensity observed in the region of the low-spin MLCT transition with increasing temperature implies an unusual partial thermal population of the low-spin state of up to about 10% at room temperature. Finally, high-spin → low-spin relaxation curves following pulsed laser excitation for [Co(terpy) 2 ](ClO 4 ) 2 dispersed in KBr discs, and as a comparison for the closely related [Co(4-terpyridone) 2 ](ClO 4 ) 2 spin-crossover compound are given.